A second police officer, Sergeant Vaughan Perry, will also be charged as a party to the alleged kidnapping.

It is alleged that he was in charge and allowed the 17-year-old to be locked in the cell, as part of a "mock arrest", at the request of Dennis.

Defence lawyer Todd Simmonds confirmed Perry would also be charged but denied any wrongdoing.

"Vaughan Perry is a proud member of the New Zealand Police and a man of absolute integrity," said Simmonds.

"He was acting at all times in accordance with the directions of a senior officer."

Both lawyers said the police officers were acting in accordance with the wishes of the whanau of the young man at the centre of the investigation - and what they believed to be his best interests.

A police spokesman said the investigation was nearing completion. "However it is still ongoing at this stage and we are unable to comment further."

Dennis, a strategic adviser in Maori affairs to the police hierarchy, made headlines this year as the chairman of Te Puea Marae in Mangere, which opened its doors to shelter families without a home.

The charitable work generated public goodwill but a political stoush began when a press secretary for Social Welfare Minister Paula Bennett leaked information about Dennis being under police investigation. The minister denied this was a deliberate smear but apologised.

Dennis was stood down September 2015 shortly after a complaint was laid by the teenage boy.

His friendship with an influential Maori family triggered the events leading to his suspension.

They disapproved of their grandson's relationship with the girl and it is claimed that they turned to Dennis for advice. A complaint was laid with the police and the boy was formally warned about underage sex.

But the relationship did not end and it is alleged that Dennis arranged for the boy to return to the Auckland Central police station. He attended, with his parents, and was told he could be charged with a sex crime if he continued seeing the girl.

Living with family in Sydney was suggested as a solution, so the teenager agreed to move there - after being put in a cell in the station.

The "mock arrest" arranged by Dennis was to show the risks and potential criminal consequences of underage sex, according to a source.

Now 18, the teen is living with his girlfriend, now 16, and her mother in a state house in Glen Innes.

The family of the boy are "extremely supportive" of Dennis.

"We are quite bewildered by the actions of his colleagues," the boy's grandfather said in July.

"Huri has done nothing but try to help us, in a Tikanga Maori way, as a family. At the core of this is a clash of cultures."